1. Field of the Invention
This invention concerns complete dentures and methods of fitting such dentures to wearers.
2. Description of the Prior Art
The major factor in the cost of prosthetic dentures at present is the difficulty involved in achieving a properly fitting denture, which fit is critical for comfort, proper mastication and appearance. Given the great variations in oral anatomy occurring among individuals and the critical nature of the fit, this fitting process has presented a very considerable technical challenge to dental science.
Very satisfactory materials for complete denture prostheses have been developed from a standpoint of durability, hardness, appearance, etc. These materials being those based on varying forms of acrylic plastics which are capable of providing the hardness and strength requirements and also of being colored to provide very aesthetically pleasing results.
However, the shaping of this material incidental to fitting of the denture to the patient's oral tissue contours by the direct molding of an acrylic plastic in its deflectable condition has heretofore been limited to reline procedures. This is due to the previous inability to confine and control the mass of material in an acceptable tray with prosthetic teeth fused to said tray, the configuration of which may be altered and shaped to fit the patient's oral anatomy. That is, in forming, some distortion of the tray would inevitably occur tending to misposition the prosthetic teeth relative each other. This would be particularly difficult in connection with the so-called "zero degree cuspal" teeth in which flat plane occlusion between the maxillary and mandibular dentures is produced, since any mislocation of the prosthetic teeth out of this plane would cause improper occlusion.
The use of deflectable acrylic as well as other alternative materials such as elastomeric materials for a tray having the prosthetic teeth molded are subject to a second even more serious drawback. Use of these materials has usually involved the bonding of the elastomeric materials to the prosthetic teeth which may be formed very satisfactorily from the aforementioned acrylic plastic or porcelain materials. However, the very considerable forces exerted on the denture during mastication by the wearer has had a tendency to open gaps between the deflectable acrylic or elastomeric material and the prosthetic teeth which allowed the entrance of food particles, with the subsequent relaxation of the forces trapping the good particles in the gaps, allowing bacterial growth and severe difficulties in maintaining the cleanliness of the dentures.
Adequate bonding of either the deflectable acrylic or elastomeric materials and the prosthetic teeth is impossible to achieve since the prosthetic materials generally do not bond to these materials in a highly satisfactory manner.
Accordingly, the conventional practice has involved complex and elaborate impression-taking procedures carried out over a period of several sessions, with a denture made to conform with the impression in order to properly fit the denture to the wearer's oral tissues. This fitting procedure accounts in large measure for the rather high expense of conventional dentures.
Attempts have been made to overcome these disadvantages, in which attempts a hard acrylic base structure is provided into which are fused the prosthetic teeth with the hard base structure receiving a deflectable thermo plastic tray bonded thereto which layer may be shaped at relatively low temperatures, compatible with human tissues to the general configuration of the patient's oral anatomy. As a final step, the molded deflectable plastic tray is lined with autompolymerizing acrylic plastic to produce a final shaping of the contour of the denture to the patient's oral cavity features. The partially set acrylic plastic is positioned within the patient's mouth, where final curing and fixating of the deflectable tray occurs.
This approach involves the use of an all-acrylic plastic structure insuring tight bonding between the deflectable tray layer and the hard base structure, but more importantly, firm anchoring of the prosthetic teeth to maintain their position during fitting and to prevent the entrance of bacteria and food particles between the prosthetic teeth and the hard base structure. Thus, this approach provides a practical but relatively quick-fitting procedure, while producing a denture having the necessary strength and stiffness requirement to preclude the deflection of the teeth and the opening of gaps in the denture into which food particles could otherwise become lodged. This denture is either used directly as a finished prosthesis or alternatively used as a model in the construction of a finished prosthesis.
This greatly reduces both the fitting and laboratory expense and thus the overall cost of obtaining the denture to the patient.
This concept utilizes, as an essential starting point, the U-shaped hard base structure in which the location of the prosthetic teeth are fixed. In the implementation of this concept, it is generally contemplated that a limited number of sizes of this hard base structure would be provided, with the molding steps of the deflectable tray accommodating the variations in maxillary or mandibular ridge configurations from that accorded by selection of sizes. While the various trays fit the majority of ridge variations, lateral positioning of the posterior teeth can be a critical factor in the ultimate success of the finished dentures. In addition, the aligning of the upper and lower teeth may not occur in severe skeletal patterns in which the lower jaw is much smaller than the upper jaw thus by the nature of size alone the teeth will not properly occlude.
Accordingly, it is an object of the present invention to provide a denture and a method of fitting such a prosthesis which allows the posterior prosthetic tooth lateral locations to be substantially altered to approximate the patient's residual gum ridge, obtaining the aforementioned advantages of a relatively simple fitting procedure in which the occlusal plane produces a hard and rigid unitary denture structure as a final result in which prosthetic teeth are securely retained so as to resist any deflecting forces, avoiding the opening of gaps such as may trap food particles.
It is another object of the present invention to produce a denture which may be provided to the patient at relatively low cost but will provide a well-fitting denture with good durability and function in terms of allowing the patient to masticate properly and which is aesthetically pleasing.